Journal Article

Overexpression of the <i>AtGluR2</i> Gene Encoding anArabidopsis Homolog of Mammalian Glutamate Receptors Impairs CalciumUtilization and Sensitivity to Ionic Stress in TransgenicPlants

Sun A Kim, JuneMyoung Kwak, Seul-Ki Jae, Myeong-Hyeon Wang and HongGil Nam

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 42, issue 1, pages 74-84
Published in print January 2001 | ISSN: 0032-0781
Published online January 2001 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pce008
Overexpression of the AtGluR2 Gene Encoding anArabidopsis Homolog of Mammalian Glutamate Receptors Impairs CalciumUtilization and Sensitivity to Ionic Stress in TransgenicPlants

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We have identified a homolog of the mammalian ionotropic glutamate receptor genes in Arabidopsis thaliana (AtGluR2). This gene was found to alter Ca2+ utilization when overexpressed in A. thaliana. These transgenic plants displayed symptoms of Ca2+ deficiency, including browning and death of the shoot apex, necrosis of leaf tips, and deformation of leaves. Supplementation with Ca2+ alleviated these phenotypes. Overall levels of Ca2+ in tissues of control plants were not significantly different from those of transgenic plants, suggesting that overexpression of the AtGluR2 gene did not affect Ca2+ uptake. However, the relative growth yield as a function of Ca2+ levels revealed that the critical deficiency content of Ca2+ in transgenic plants was three times higher than that of control plants. The transgenic plants also exhibited hypersensitivity to Na+ and K+ ionic stresses. The ion hypersensitivity was ameliorated by supplementation with Ca2+. The results showed that overexpression of the AtGluR2 gene caused reduced efficiency of Ca2+ utilization in the transgenic plants. The promoter of the AtGluR2 gene was active in vascular tissues, particularly in cells adjacent to the conducting vessels. This suggests that AtGluR2 encodes a functional channel that unloads Ca2+ from the xylem vessels. The results together suggest that appropriate expression of the AtGluR2 protein may play critical roles in Ca2+ nutrition by controlling the ion allocation among different Ca2+ sinks both during normal development and during adaptation to ionic stresses.

Keywords: Key words: Arabidopsis thaliana — Calcium efficiency — Critical deficiency content — Glutamate receptor homolog — Ion hypersensitivity — Xylem unloading.; Abbreviations: AtGluR2, Arabidopsis thalianaglutamatereceptor homolog 2; B5 medium, Gamborg B5 medium; CDC, criticaldeficiency content; EST, expressed sequence tag; GUS, β-glucuronidase; iGluR,ionotropic glutamate receptor; NCBI, National Center for BiotechnologyInformation.; The nucleotide sequences reported in this paper have been submitted tothe GenBank under accession numbers AF159498 andAF159499.

Journal Article.  6062 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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